LMP7 is an essential component of the immunoproteasome, mainly expressed in immune cells such as T/B lymphocytes and monocytes, as well as non-immune cells that have exposed to inflammatory cytokines, including IFN-γ and TNFα. Immunoproteasome plays an essential role in generation of antigenic peptide repertoire and shaping MHC class I restricted CD8+ T cell response. Moebius J. et al. European Journal of Immunology. 2010; Basler, M. et al. Journal of Immunology. 2004. 3925-34. Emerging data suggested that LMP7 also regulate inflammatory cytokine production and immune cell functions beyond the regulation of MHC class I mediated antigen presentation.
A small molecule LMP7 inhibitor, PR-957, has been shown to potently block Th1/17 differentiation, B cell effector functions and production of inflammatory cytokines (IL-6, TNF-α, IL-23). Muchamuel T. et al. Natural Medicine. 2009. 15, 781-787; Basler M. et al. Journal of Immunology. 2010, 634-41.
In addition, LMP7 blockade with PR-957 has been demonstrated to produce therapeutic benefits in several preclinical autoimmune disease models. First, PR-957 was demonstrated to significantly decrease disease score in mouse CAIA and CIA arthritis models, with hallmarks of significantly reduced inflammation and bone erosion. Muchamuel T. et al. Natural Medicine. 2009. 15, 781-787. In addition, PR-957 reduced plasma cells numbers and levels of anti-dsDNA IgG in MRL/lpr lupus-prone mice model, and prevented disease progression in these mice. Ichikawa H T, et al. Arthritis & Rheumatism. 2012. 64, 493-503. Furthermore, PR-957 reduced inflammation and tissue destruction in a DSS-induced colitis model in mice. Basler M. et al. Journal of Immunology. 2010, 634-41. Lastly, LMP7 knockout mice had also been shown to be protected from disease in IBD models. Schmidt N. et al. Gut 2010. 896-906.
Taken together, data strongly suggests that LMP7 activity is closely related to the functions of B/T lymphocytes and production of inflammatory cytokines, all of which are clinically validated targets/pathways in the pathogenesis of rheumatoid arthritis, lupus and IBD. Thus, existing data have provided strong rationale for targeting LMP7 for autoimmune disease indications. Due to potential liability with long term usage of a covalent inhibitor in chronic diseases like autoimmunity, a covalent reversible or non-covalent small molecule LMP7 inhibitor is highly desired for autoimmune disease indications.